The prior art tire pressure gauge is generally composed of a pressure measuring head and a guide tube. The pressure measuring head is provided with a protruded rod and an air hole. The guide tube is connected with the pressure measuring head and used to house therein a piston, a pressure-bearing spring, a scale, and a plug. Such a conventional tire pressure gauge as described above is defective in design in that the pressure measuring head and the guide tube can not be connected intimately after having been assembled and disassembled several times, thereby resulting in a leak in the seam between the pressure measuring head and the guide tube. In addition, it is inconvenient to use the prior art tire pressure gauge at night in a poorly lighted place because the prior art tire pressure gauge is not provided with a lighting fixture.